There is known a control apparatus for a hybrid vehicle provided with an engine and electric motors serving as a vehicle drive power source, a power transmitting system for transmitting a drive force of the vehicle drive power source to a drive wheel, and an electric-energy storage device for supplying a stored electric energy to the electric motor. Patent documents 1, 2 and 3 disclose examples of such a hybrid vehicle control apparatus. The hybrid vehicles disclosed in these documents are provided with a power transmitting system including a planetary gear set which has a first element connected to the engine, a second element connected to a first electric motor, and a third element connected to an output rotary member and a second electric motor. The planetary gear set is configured to distribute an output of the engine to the first electric motor and the output rotary member. These hybrid vehicles are able to run in a motor drive mode in which only the second electric motor is operated as the vehicle drive power source, while the engine is held at rest. Generally, the hybrid vehicles as described above are provided with a mechanically operated oil pump operatively connected to the engine and constructed to deliver a working oil according to an operation of the engine, so that the oil pump operated while the engine is operated supplies a lubricant to the above-described planetary gear set and other parts (such as gears and bearings) of the power transmitting system.
The oil pump connected to the engine is not operated in the motor drive mode in which the engine is held at rest, so that the lubricant is not supplied as needed to the predetermined parts of the above-described power transmitting system in the motor drive mode, giving rise to a risk of deterioration of durability of the predetermined parts (such as the gears and other rotating members) of the power transmitting system, due to metal contacts of the parts, etc. In particular, a so-called “plug-in hybrid vehicle” the electric-energy storage device of which is chargeable with an electric energy supplied from an external electric power13ource for the hybrid vehicle such as a domestic power source is considered to be able to have comparatively long running time and distance in the motor drive mode, and consequently has a high risk of the above-described problem caused by the long running in the motor drive mode in which the lubricant is not supplied with the engine held at rest. To deal with this problem, the above-described Patent document 1 proposes a forced operation of the engine (engine motoring) by the first electric motor to operate the oil pump to supply the lubricant to predetermined parts of the engine, when a time period of resting of the engine exceeds a predetermined upper limit.